First FeII-based supramolecular cage with pyridine-hydrazone coordination sites and large cavity volume (306 Å3) exhibits temperature induced spin crossover behaviour.

Synthetic nitrogenases, that are transition metal complexes capable of reducing N 2 to NH 3 at atmospheric pressure, are considered as alternatives for the Haber−Bosch process; however, the currently studied complexes deactivate rapidly. Experimental studies on different types of artificial nitrogenases suggest that there exists a universal deactivation mechanism via the formation of catalytically inactive metal hydrides. In the present computational study, we examine whether the coordination of H 2 , which leads to hydride formation, can be suppressed by the proper tuning of the ligand field. Using the trisphosphino-E (E = borate, alkyl, or silyl) ligated iron nitrogenases as model systems, we investigate the effect of introducing common substituents on the relation between the binding affinity of N 2 and that of H 2 . We find that the Gibbs free energy of H 2 and N 2 coordination strongly correlate, as the desired decrease of H 2 affinity can only be achieved at the cost of an undesired decrease in N 2 affinity. This interdependence can be interpreted by orbital analysis, which reveals that the coordination of N 2 and H 2 comes with similar interactions toward the d orbitals of the Fe center. We conclude that the continuous removal of H 2 from the reaction mixturerather than the redesign of the catalystis the effective way of eliminating H 2 -induced catalyst poisoning.